When an attenuating function, a polarizing function, a scattering function, a light-shielding function, or the like is required for an irradiated light such as laser light and natural light, apparatuses have conventionally been adapted, which operate based on principles different from each other, depending on the functions. Thus, the products corresponding to the functions have been prepared by the production processes different from each other, depending on the functions.
For example, in LCD (Liquid Crystal Display), in order to control optical rotary power or birefringent property in display, a linear polarizing plate or a circular polarizing plate is used. Also in OLED (organic electroluminescence element), the circular polarizing plate is used to prevent the reflection of light from outside. Heretofore, for such polarizing plates (polarizing elements), iodine has been widely used as a dichroic material. However, in the case where iodine is used for the polarizing element, heat resistance and light fastness thereof are not sufficient since iodine has a large sublimation property. Further, the extinction color becomes deep blue, and an ideal achromatic color polarizing element in the entire visible spectral region cannot necessarily be obtained.
Thus, a polarizing element has been studied, in which an organic dye has been employed as the dichroic material. However, in employing the organic dyes, there is a problem, for example, that only polarizing elements are obtained, which is distinctly inferior in dichroic property to those employing iodine. Particularly, in LCD using optical rotation or birefringent property of light as the principle of display, the polarizing element is an important constituent. In recent years, in order to improve the performance of display or the like, the development of a novel polarizing element has been preceded.
As a method of forming such polarizing element, a method has been proposed, in which, in the same manner as in the case of a polarizing element containing iodine, an organic dye having dichroism (dichroic dye) is dissolved in or adsorbed to a polymer material such as polyvinyl alcohol, and the film thereof is stretched in one direction to be a film shape so that the dichroic dye is oriented. However, in this method, there is a problem, for example, that time and effort are required for steps such as a stretching treatment.
Thus, in recent years, other methods have attracted an attention. As such method, Non-Patent Literature 1 describes a method, in which a dichroic dye is aligned on a substrate such as a glass or a transparent film by utilizing the intermolecular interaction of organic dye molecules or the like, to form a polarizing film (anisotropic dye film). However, it has been known that there has been a problem in the heat resistance in the method described in the literature.
Further, a wet film-forming method achieves orienting a dichroic dye on the substrate such as a glass or a transparent film by utilizing the intermolecular interaction of organic dye molecules or the like. In the case where an anisotropic dye film is prepared by the wet film-forming method, the dye to be used in the dye film are required not only to have the high dichroism of the dye molecules but also to be a dye suitable for the process of the wet film-forming method. Examples of the process in the wet film-forming method include the process of disposing and orientating the dye on the substrate or the process of controlling the orientation. Accordingly, there are many cases that even the conventional dyes, that may be used in the polarizing elements underwent the above-mentioned stretching treatment, are not suitable for the wet film-forming method. On the other hand, Patent Literatures 1 to 3 propose materials suitable for the above-described process. However, although such materials are suitable for the process, they have had a problem that they have not been able to show high dichroism.
Further, Patent Literature 4 proposes a dye represented by chromogen (SO3M)n as a material suitable for the process. In the literature, the achromatic color is shown by combining several kinds of dichroic dyes. However, in the case where an anisotropic dye film is obtained by combining the several kinds of dichroic dyes, there is a problem that since different molecules are mixed, the orientation of the molecules is disturbed and obtaining a high dichroism is difficult.
Further, Patent Literature 5 describes that a light absorption anisotropic film prepared by the wet film-forming method is prepared, and also describes a dichroic dye represented by the following structural formula as an example of the dichroic dye that can be used.

However, the compound has a problem that the dichroism and the absorbance at a long-wavelength region are insufficient.